The present invention relates to an image forming apparatus provided with an automatic writing-position determination means for always forming an image at a correct position on the recording material, by correcting an image writing-position corresponding to an offset of the recording material, according to the detection result obtained by detecting an offset of the recording material.
The correction of the image writing-position is the control to change the start position of writing by the writing means 3, 4 corresponding to the end positions. X, Xxe2x80x2 when the recording materials 10a and 10b are supplied onto the photoreceptor 1 respectively with the end positions X, Xxe2x80x2, as shown in FIG. 9, and controlled as described above, by the automatic writing-position determination means.
An image forming apparatus, in which the automatic writing-position determination means is assembled, is disclosed in, for example, Japanese Patent No. 2550558, or Japanese Tokuganhei No. 11-77728 specification. The image forming apparatus disclosed in Japanese Patent No. 2550558 detects the offset of the recording material by a plurality of detection elements, and according to the detection results, corrects the position of the image data in a memory. Because the resolving power of the offset detection corresponds to the number of the detection elements, the resolving power of the offset detection is limited. However, the image forming apparatus disclosed in Japanese Tokuganhei No. 11-77728 detects the offset by a detection resolving power of more than 0.25 mm, and corrects the offset with a highly accurate offset correction by fully using the control capability of the writing-position which is owned by the digital writing means such as the writing means by a laser light emitting element.
As described above, in the automatic writing-position determination means disclosed in Japanese Tokuganhei No. 11-77728, the resolving power of the end position detection means is matched with that of the writing means, and the high accuracy offset correction equal to the resolving power of the writing means can be conducted. However, when the automatic writing-position determination means is actually used, there are various problems.
An image position on the recording material when an image is written on the recording material by laser writing as an example, will be described below.
The image position in the main scanning direction at the time of writing, is controlled by adjusting the writing start position in the main scanning direction of writing by the laser, and in the sub-scanning direction, it is controlled by adjusting the timing of the conveyance of the recording material and writing. The position of the writing start in the main scanning direction is determined by the calculation from the offset information from the end position detection means and the information of the size of the recording material. However, the recording materials used for the image formation are various in size and kind. Because there is a case in which the detection of the position of the recording material is difficult, and also a case in which the recording material with the irregular type size apart from the regular type size is used, there is a case where the offset correction by the automatic end position detection means is difficult, and highly reliable offset correction is not conducted.
To overcome the abovementioned drawbacks in conventional image forming apparatus, it is an object of the present invention to solve the above problems in the offset correction using the automatic writing-position determination means, and to provide an image forming apparatus provided with the automatic writing-position determination means by which the offset correction can be conducted with the high accuracy, and the highly reliable automatic writing-position determination is conducted.
Accordingly, to overcome the cited shortcomings, the abovementioned object of the present invention can be attained by image forming apparatus described as follow.
(1) An image forming apparatus, comprising: an image forming section to form an image by writing each of scanning lines; an end position detecting section to detect an end position of a recording material in a direction orthogonal to a conveyance direction of the recording material conveyed to an image forming position; and a selecting section to select either an automatic writing-position determining mode or a predetermined writing-position determining mode, wherein, when the selecting section selects the automatic writing-position determining mode, the image forming section commences an image writing action from a writing start position determined on the basis of a detected result of the end position detecting device, while, when the selecting section selects the predetermined writing-position determining mode, the image forming section commences the image writing action from a predetermined writing start position set in advance.
(2) The image forming apparatus of item 1, wherein the selecting section includes an automatic selector.
(3) The image forming apparatus of item 1, wherein the selecting section includes a manual selector.
(4) The image forming apparatus of item 1, further comprising: a plurality of sheet feeding sections, wherein, when a specific sheet feeding section included in the plurality of sheet feeding sections is currently employed, the selecting section selects the automatic writing-position determining mode, while, when a sheet feeding section, included in the plurality of sheet feeding sections other than the specific sheet feeding section, is currently employed, the selecting section selects the predetermined writing-position determining mode.
(5) The image forming apparatus of item 1, further comprising: a discriminating section to discriminate a kind of the recording material to be used, wherein, when the discriminating section determines that a specific kind of the recording material is currently used, the selecting section selects the predetermined writing-position determining mode, while, when the discriminating section determines that a kind of the recording material other than the specific kind of the recording material is currently used, the selecting section selects the automatic writing-position determining mode.
(6) The image forming apparatus of item 1, wherein, when image data for forming the image includes such data that possibly cause an error in detecting the end position of the recording material in a direction orthogonal to the conveyance direction, the selecting section selects the predetermined writing-position determining mode.
(7) The image forming apparatus of item 1, wherein the image forming apparatus is provided with a duplex image forming mode in which a reverse side image is formed on a reverse side of the recording material after an obverse side image is formed on an obverse side of the recording material, and when the reverse side image is formed on the reverse side of the recording material, on the obverse side of which the obverse side image is already formed in the predetermined writing-position determining mode, the selecting section selects the predetermined writing-position determining mode.
(8) The image forming apparatus of item 1, further comprising: a size detecting section to detect a size of the recording material, wherein, when the selecting section selects the predetermined writing-position determining mode, the image forming section commences the image writing action based on a detected result of the size detecting section.
(9) The image forming apparatus of item 1, wherein the image forming section commences the image writing action based on data of writing start positions, which were determined in image forming operations in the past.
(10) An image forming apparatus, comprising: a conveyance section to convey a recording material; an end position detecting section to detect an end position of a recording material in a direction orthogonal to a conveyance direction of the recording material; an edge detecting section to detect a leading or a trailing edge of the recording material; and a triggering section to trigger the end position detecting section, wherein the triggering section includes an offset detecting device to trigger the end position detecting section based on a signal outputted by the edge detecting section or an operating action of the conveyance section.
(11) The image forming apparatus of item 10, wherein either a first mode in which the triggering section triggers the end position detecting section based on the signal outputted by the edge detecting section, or a second mode in which the triggering section triggers the end position detecting section based on the operating action of the conveyance section, can be set by an external operation.
(12) The image forming apparatus of item 10, wherein either a first mode in which the triggering section triggers the end position detecting section based on the signal outputted by the edge detecting section, or a second mode in which the triggering section triggers the end position detecting section based on the operating action of the conveyance section, is automatically selected.
(13) The image forming apparatus of item 11, further comprising: a detecting section to detect a kind of the recording material, wherein either the first mode or the second mode is selected, based on a detected result of the detecting section.
(14) The image forming apparatus of item 13, wherein the kind of the recording material is a size of the recording material.
(15) The image forming apparatus of item 12, further comprising: a detecting section to detect a kind of the recording material, wherein either the first mode or the second mode is automatically selected, based on a detected result of the detecting section.
(16) The image forming apparatus of item 15, wherein the kind of the recording material is a size of the recording material.
(17) The image forming apparatus of item 10, wherein the conveyance section includes a synchronized conveyance device to convey the recording material to an image forming position so as to be synchronized with an image forming operation, and the triggering section triggers the end position detecting section based on control signals for controlling the synchronized conveyance device.
(18) An image forming apparatus, comprising: an image forming section to form an image by writing each of scanning lines, starting from a writing start position; a conveyance section to convey a recording material; an end position detecting section to detect an end position of a recording material in a direction orthogonal to a conveyance direction of the recording material; an edge detecting section to detect a passage of a leading or a trailing edge of the recording material; a triggering section to trigger the end position detecting section based on a signal outputted by the edge detecting section or an operating action of the conveyance section; and a selecting section to select either an automatic writing-position determining mode in which the writing start position is determined, based on a detected result of the end position detecting section, or a predetermined writing-position determining mode in which the writing start position is determined, corresponding to a predetermined writing start position set in advance.